package day33;

// 客似云来
// 其实就类似于Fib
// 1 1 2 3 5 ...

/* 存在错误！！

import java.util.Scanner;

public class Main2 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNextInt()) {
            int from = in.nextInt();
            int to = in.nextInt();
            long first = 0;
            long second = 1;
            long guest = 1;
            if((from>=1) && (to>=from) && (to<=80)) {
                // 首先计算第from天的客人
                for (int i = 1; i <= from; i++) {
                    guest = first + second;
                    first = second;
                    second = guest;
                }
                // 第form到to的合计
                for (int i = from+1; i <= to; i++) {
                    long third = first + second;
                    first = second;
                    second = third;
                    guest += third;
                }
            }
            System.out.println(guest);
        }
    }
}*/


// 使用数组
// 修改版本：通过

import java.util.Scanner;

public class Main2 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNextInt()) {
            int from = in.nextInt();
            int to = in.nextInt();
            long guest = 0;
            long fib[] = new long[81];
            fib[0] = 0;
            fib[1] = 1;
            // 首先进行计算
            for (int i = 2; i < 81; i++) {
                fib[i] = fib[i-1] + fib[i-2];
            }
            // 开始进行判断
            if((from>=1) && (to>=from) && (to<=80)) {
                for (int i = from; i <= to; i++) {
                    guest += fib[i];
                }
            }
            System.out.println(guest);
        }
    }
}